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Resources and Shifts
Blocks of interest
Items will sometimes require resources before they can proceed to the next step in a process. For example, a car might need an attendant to drive it through the car wash, a vendor’s invoice could require a receiving report before payment is made, or parts might need to be assembled by a worker. Resources provide a service to the items in a model; their availability or lack thereof can cause constraints on the flow of items.
One of the main reasons to model a process is to analyze resource availability and utilization and to determine the impact of resource constraints on the system’s capacity. This tells how efficiently current resources are being used and what happens if they will not be available or when there is a wait for them to become available. Often the objective is to try to improve resource utilization without causing overly long waiting lines or to determine how to reduce waiting lines without adding more resources.
This chapter discusses:
• Modeling resources with the Resource Pool block
• Modeling resources using the Resource Item block • Othermethodsformodelingresources
• Closed and open systems
• Ways in which resources can be scheduled
• ControllingresourcesandactivitieswiththeShiftblock
• Advanced Resource Management and setting up resource requirements
☞ The models illustrated in this chapter are located in the folder \Examples\Discrete Event\Resources and Shifts.
Blocks of interest
The following blocks are the main focus of this chapter. Each block’s library and category appears in parentheses after its name.
Resource pool blocks
Resource Manager (Item > Resources)
Manages and controls the behavior and utilization of advanced resources. Use this
block to create, modify, view and delete Advanced Resources. This block creates inter- nal databases where it stores all of the information needed to manage and control Advanced Resources. See “Advanced Resource Management” on page 238.
☞ The Resource Manager block is an advanced tool that is available in the ExtendSim Suite and ExtendSim AT packages only.
Resource Pool (Item > Resources)
Stores a count of resources for the model. The resources are taken by the Queue block
(in “resource pool queue” mode) and released by the Resource Pool Release block at some later point in the model.
Queue (Item > Queues)
When the Queue type is set to “resource pool queue”, items wait here for required
resource pool units from the Resource Pool block. Once the needed resource units are available, the block checks for downstream capacity before releasing items.
Discrete Event